The objectives of this project fall into categories as follows: 1. To investigate the genetic and population aspects of the Gm and Inv allotypes in man, to provide a better insight into the evolution of man, and to learn more about the genetics of antigens. The latter includes searching for new factors. 2. To determine the relation of the antigens to the structure of the IgG molecules to gain a better understanding of genetic control of polypeptides and of the nature of antibodies. 3. To continue a search for the selection factor(s) responsible for the racial and geographic distribution of the allotypes in man. 4. To extend earlier studies on the relation of the antibodies against the Gm and Inv factors to the rheumatoid factor.